344 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



The nature of tlie add. tentaculi has already been considered, it 

 being merely a separation of the deeper fibres of the add. mand. 

 The lev. arc. pal. is plainly derived from a constrictor, but its 

 function has been changed by the development of osseous structures, 

 so that instead of assisting in the contraction of the pharyngeal 

 cavity, it enlarges it by raising the hyomandibular apparatus, etc. 

 The reason why a trigeminal muscle should act as the opponent of 

 muscles supplied by the seventh nerve, is that the forward growth 

 superficially of the hyoidean muscles was prevented by the presence 

 in primitive forms of the spiracle. The dil. operc. is evidently a 

 portion of the lev. arc. pal. adapted to the necessities of the opercular 

 apparatus. The incongruity between its action and its innervation 

 is even more apparent than in the lev. arc. pal.^ but is explicable in 

 the same way as Vetter has pointed out. 



The intermandibularis is without doubt the representative of the 

 most anterior ventral portions of the Selachian constrictor. It is 

 supplied by both the fifth and the seventh nerve, and instead, there- 

 fore, of being assigned to the group of muscles supplied by the fifth 

 nerve, as Vetter has done, it must be considered as representing the 

 ventral portion of a constrictor layer lying between the palatine and 

 mandibular and the mandibular and hyoidean arches. The anterior 

 moiety of such a layer would be supplied by the fifth, and the pos- 

 terior by the seventh nerve. In the Teleosts this layer has con- 

 tracted in breadth very much, until it forms merely a narrow band 

 between the extremities of the mandibular arch, but, with the grad- 

 ual narrowing, there has been, so to speak, a corresponding lengthen- 

 ing out of the innervating branch from the facialis and a shortening 

 of that from the trigeminus, so that even when limited to the mandi- 

 bular arch it still possesses its hyoidean nerve. 



Just as all the muscles of the mandibular arch (i.e., those supplied 

 by the fifth nerve), are derived from a constrictor, so are all those of 

 the hyoid arch, (i.e., those supplied by the seventh nerve.) The add. 

 arc. pal. has apparently an abnormal position, extending between the 

 skull and the palatine, metapterygoid and hyomandibular, thus com- 

 ma- into relation not only with the arches to which it belongs but also 

 with the arch in front of it. The only explanation to be given for 

 this is that the muscle has extended its insertion forwards as neces- 

 sity required it. In Amiurus, owing to the necessity for motion of 

 the palatine for the purpose of erecting (abducting) the tentacle sup- 



